Exam #2 - June 29, 2000

The Jovian Planet Systems, Small Bodies, and the Formation of the Solar System

Astronomy 1110

Dr. Henry Throop, University of Colorado

"In order for a scientific revolution to occur, most scientists have to be wrong." -- unknown

Formulas & Numbers

Kepler's 1st law: All planets move in ellipses, with the Sun at one focus.
Kepler's 2nd law: The orbit of each planet sweeps out equal area in equal time.
Kepler's 3rd law: (orbital period in yr)2 = (average distance in AU)3, for bodies orbiting the sun.
Kepler's 3rd law: (orbital period in s)2 = 4 pi2 (average distance in cm)3 / (G (M1 + M2))
Newton's law of gravity: F = G (Mass 1) (Mass 2)/(distance)2
1 AU = 150 million km (1.5 108 km = 1.5 1013 cm)
1 km = 103 m = 105 cm = 106 mm
Speed of light = c = 3 1010 cm/s
Light year = 1 1018 cm
Velocity = Distance / Time

Instructions: There are 20 questions. The first set should be done on the bubble form, and the second and third sets on the test itself. If you are unclear on anything, please talk to me or Rob. The exam is due at the end of class, 12:35 PM.

Multiple Choice (30 points @ 3 points each)

1. Jupiter's moon Io is the most actively volcanic body in the solar system. Why was this surprising when it was discovered?
a) Io is not fully differentiated.
b) Ganymede has a strong magnetic field, and is probably warm inside.
c) Jupiter is a long distance from the sun, and thus cold.
d) Galileo had not predicted this when he observed the moons of Jupiter.

2. The greenhouse effect
a) Affects the Jovian planets' upper atmospheres.
b) Only works for terrestrial planets, near the Sun.
c) Makes Jupiter's core much warmer.
d) Must be stopped!

3. Jupiter's core can reach temperatures over 20,000 K. What causes these high temperatures?
a) Tidal heating
b) Core dumping and unsuccessful rebooting
c) Radioactive decay
d) Differentiation

4. The Mars Climate Orbiter dramatically crashed into the planet's surface on September 23, 1999, due to a unit conversion error in a short software code that converted foot-pounds into newton-meters, English to Metric. This mission cost about $100 million. About how many such Mars missions could be launched to equal the cost of one launch of the Space Shuttle?
a) two
b) four
c) ten
d) forty

5. Compared with a planet made of purely ices, a planet made of equal parts ices, metals, and rocks is probably
a) less dense
b) more dense
c) depends on the mass
d) brighter

6. The process by which heat escapes from the Earth's interior is
a) Convection
b) Differentiation
c) Astigmatism
d) Tidal heating

7. The densest materials in the solar system condense from their gas to solid state at...
a) The highest temperatures
b) The lowest temperatures
c) Depends on their distance
d) Can't tell

8. Assuming Pluto formed at its current location, does the solar nebula model predict we would find metals in Pluto?
a) No - metals condense only in the inner solar system.
b) Yes - metals condense almost anywhere.
c) Any metals were probably brought in from elsewhere.
d) Pluto is icy, but Charon probably metallic.

9. Saturn's rings are primarily
a) Atmospheric gasses thrown off by the planet's rotation.
b) Destroyed lost spacecraft sucked away from Mars.
c) Broken up remains of comets, moons, and asteroids.
d) On highly elliptical orbits.

10. A recent headline in the National Enquirer proclaimed, "New Galaxy Shaped Like a Gigantic...
a) Pinwheel!"
b) Fetus!"
c) Rhinestone!"
d) Crucifix!"

Short Answer Questions (30 points @ 5 points each)

1. Jupiter can retain hydrogen in its atmosphere, but in our atmosphere, hydrogen rapidly escapes to space. What are two reasons why Jupiter can retain this gas?




2. Saturn is over 120,000 km across, but we've can see through less than 1% of it directly. List three ways we can figure out what's inside it.




3. Jupiter takes about 12 years to orbit the sun, and at one part of the asteroid belt, an asteroid takes 6 years to orbit. Describe (briefly) why this asteroid might be an interesting one to watch.




4. Your friend Halley says that she was making flapjacks for breakfast last summer and saw a comet high overhead, with its tail pointed toward Denver (from Boulder). Do you believe her? Why or why not?




5. The Earth has a moon, but Venus doesn't. Propose a reason for this.




6. Extrasolar planets have been discovered orbiting nearly 50 stars, but we've never been able to directly image most of them. Why not?




Long Answer Questions (40 points @ 20/10/10 points each)

1. (20 points) Broadly summarize the differences between the terrestrial planets (TP's) and the Jovian planets (JP's). You should include aspects of their size, composition, formation history, heat sources, and satellites, as well as other things which could be considered important. You need not talk about individual planets (Earth, Saturn, etc.) unless you'd like to. Ignore Pluto, who is being difficult.





2. (10 points) Let's say we were to point our telescopes up to the star Astro-1110, and were able to witness a solar system being formed in front of our eyes. We observe two things about Astro-1110: a) the nebula is much hotter than ours ever was (ices can't condense at its outer edge and never will, but rocks and metals can throughout) and b) its solar wind is much weaker than our Sun's, and always will be. If we assume everything else about the star and its nebula is the same as our own, describe the planetary system that will form. You can assume the positions and sizes of the rocky planetesimals formed are the same as in our system.





3. (10 points) The four `Galilean Satellites' (or `Medicean Stars', as Galileo called them) are fascinating worlds. Pick two of them and write about them: what do they look like, what's happening on their surfaces, what's happening in their cores (why?), and what's a major question that you'd like to answer about them?


Dr. Henry Throop, University of Colorado / throop@broccoli.colorado.edu

Last modified 28-Jun-2000